Refrigeration systems are utilized to produce a lower temperature in a predetermined space, such as within a chamber or a room, relative to an ambient temperature. In many refrigeration systems, temperatures lower than ambient are achieved through the compression and expansion of a refrigerant. In particular, an evaporator transfers heat from the predetermined space or its contents to a refrigerant in a vaporized state. The vaporized refrigerant is communicated to a compressor. The compressor increases the pressure of the vaporized refrigerant, which acts to increase the temperature of the vaporized refrigerant. A condenser transfers heat from the refrigerant, typically to the ambient environment, causing the refrigerant to condense to a liquid form. The liquid form of the refrigerant is communicated to an input of an expansion valve which reduces the pressure and temperature of the refrigerant. The refrigerant, back in a vaporized form, is communicated from an output of the expansion valve back to the evaporator. The refrigerant is communicated within the refrigeration system using tubing or like plumbing components.
A number of issues are involved in controlling a refrigeration system. These issues include: how to control motors associated with the refrigeration system (e.g. a compressor motor); how to define and control a refrigeration cycle; and how to define and control a defrost cycle.